The main semiconductor devices in integrated circuits, especially in very-large-scale integrated circuits, include metal-oxide-semiconductor (MOS) transistors. With continuous development of the fabrication technology of integrated circuits, the semiconductor technology node steadily shrinks and the geometry dimension of semiconductor structures continuously decreases following the Moore's law. When the dimension of semiconductor structures shrinks to a certain value, various secondary effects due to approaching the physical limit of the semiconductor structures may emerge successively. Further scaling down the feature size of semiconductor structures becomes more and more difficult. Specifically, in the field of semiconductor fabrication, one of the most challenging issues is to solve the problem of having a large leakage current in semiconductor structures. A main reason for such a large leakage current is the continuous decrease of the thickness of the gate dielectric layer in traditional semiconductor structures.
Currently, a method proposed to reduce the leakage current is to use a high-k dielectric material to replace the traditional SiO2 dielectric material while use a metal to form the gate electrode. Specifically, using a metal, instead of a traditional gate electrode material, to form the gate electrode may avoid the Fermi energy pinning effect between the traditional gate electrode material and the high-k dielectric material. In addition, using a metal to form the gate electrode may also avoid the boron diffusion effect. Therefore, the introduction of high-k metal gate (HKMG) may reduce the leakage current in semiconductor structures.
Although introducing HKMG may, to some extent, improve the electrical performance of semiconductor structures, many aspects of existing semiconductor structures and fabrication methods still need to be further improved. The disclosed semiconductor structures and fabrication methods thereof are directed to solve one or more problems set forth above and other problems in the art.